This invention relates to magnetoresistance effect elements using a multilayered magnetic thin film with high magnetoresistance effect, and particularly to magnetoresistance-effect elements, magnetic heads and magnetic storage apparatus for achieving high-density recording on a magnetic recording medium on which narrow tracks are formed.
An investigation is now being made of magnetic heads using the magnetoresistance effect for high density-magnetic recording. At present, an alloy film of Ni-20 at % Fe is used for the magnetoresistance effect material. However, a magnetoresistance effect element using the Ni-20 at % Fe alloy film often causes noise such as Barkhausen noise, and thus other magnetoresistance effect materials are also under investigation.
On the other hand, recently Suezawa, et al. have reported a magnetoresistance effect film which utilizes the ferromagnetic spin-dependent tunneling phenomenon and which detects magnetic flux from the electrical resistance change of a multilayered film having a pair of magnetic layers divided by an insulating layer, as is disclose in Proceedings of the International Symposium on Physics of Magnetic Materials, Apr. 8-11, 1987, pp. 303-306. This report has introduced a multilayered structure of a Ni/NiO/Co junction and multilayered films of Al/Al2O3/Ni, Coxe2x80x94Al/Al2O3/Ni exhibiting the ferromagnetic spin-dependent tunneling effect. However, in either case, the junction area between the pair of magnetic layers is as wide as about 1 mm2, and the relative resistivity change, xcex94xcfx81/xcfx81 is as small as about 1% at room temperature. In addition, since the element structure shown in this example is not capable of sensing a small magnetic flux change, it is impossible to precisely detect the change of magnetic flux leaking from a magnetic recording medium recorded at a high density.
In the prior art, a Ni/NiO/Co multilayer, for example, has an Ni layer and a Co layer of a rectangular shape made perpendicular to each other to allow all current to pass the NiO layer to effectively detect the resistance change due to the ferromagnetic spin-dependent tunneling effect. However, when used for a magnetic head, the intersection of the ferromagnetic Ni layer and Co layer will be insufficient to precisely detect the magnetic field in a narrow region because the longitudinal direction of either magnetic layer is parallel to the surface of the magnetic recording medium. In other words, the magnetic flux change associated with the signal recorded in a narrow track cannot be detected with a high sensitivity.
Moreover, the ferromagnetic spin-dependent tunneling effect of an Fe/C/Fe multilayer has been reported by J. C. Slonczewski in Phys. Rev. Vol. B39, pp. 6995, 1989, xe2x80x9cConductance and Exchange Coupling of Two Ferromagnets Separated by a Tunneling Barrierxe2x80x9d.
In the application of the ferromagnetic tunneling film to the magnetic heads, the ferromagnetic tunneling film is required not to deteriorate in its characteristics in the course of the magnetic head producing process. The magnetic head producing process often includes a heating process. However, when the Fe/C/Fe multilayer film is heated to 300xc2x0 C. or above, carbon C is diffused into the Fe layer, thus deteriorating the characteristics. Also, when the intermediate layer is made of an oxide such as NiO or Al2O3, the interface energy increases in the interface between the magnetic layers and the intermediate layer. The increase of the interface energy will act to decrease the number of atoms in the interface, thus causing defects such as vacancies in the intermediate layer and magnetic layer, so that the soft magnetic characteristics may be deteriorated as described by Nakatani, et al. in J. Appl. Phys., Vol. 66, pp. 4338, 1989, xe2x80x9cChanges in Soft Magnetic Properties of Fe Multilayered Films due to Lattice Mismatches between Fe and Intermediate Layersxe2x80x9d.
Moreover, an Fe/Cr multilayered film has recently been reported, of which the relative resistivity change is about 50% as described in Physical Review Letters, Vol. 61, No. 21, pp. 2472 to 2475, 1988.
In the magnetoresistance effect element having such a multilayer structure as the Fe/Cr multilayered film, the electrical resistance is changed by the magnetic field when electrons are moved from a magnetic layer to another magnetic layer, or passed through a non-magnetic intermediate layer. At this time, the current is flowed in the film-thickness direction. However, the film thickness of the magnetic film is several hundreds of nm or below and the element resistance is low. Thus, the rate of resistance change is high, but the amount of resistance change is small. When this film is applied to an actual magnetic sensor or magnetic head, the output is small.
Also, in the magnetic disk apparatus, magnetic heads are used for writing and reading information on and from a magnetic recording medium, and in this case the electromagnetic induction-type ring head, for example, is widely used for the magnetic head for writing and reading. In a rigid-type magnetic disk apparatus for a computer, an induction current is flowed in the magnetic head which is floated with a very small gap from the surface of a disk-like magnetic recording medium rotating at a high speed, so that the magnetic field generated at the tip of the magnetic head can enable recording on the magnetic recording medium. As the recording density is improved so that the recorded bits are small, it has been demanded to use a magnetic head having a high writing and reading efficiency. In the prior art, the same ring head has been used for writing and reading, but no dual elements are used for an inductive-write and magnetoresistant-read dual-element magnetic head for improving their functional efficiency. An example of this dual-element magnetic head is disclosed in Japanese Patent laid-open Gazette No. JP-A-51-44917. For the dual-element magnetic head, it is desired to use elements having a particularly high-sensitivity reading function, in which case the magnetic detecting element using the magnetoresistance effect (Japanese Patent Publication No. JP-B-53-17404) and the magnetic detecting element using the magnetosensitive transistor (Japanese Patent Laid-open Gazette No. JP-A-57-177573) are proposed. However, these elements do not have enough magnetic detection sensitivity for high-density magnetic recording over 100 Mb/in2.
Accordingly, it is an object of the invention to provide a magnetoresistance effect element capable of sensing a very small change of magnetic flux from a narrow region of a magnetic recording medium with high sensitivity and with high resolution.
It is another object of the invention to provide a magnetoresistance effect element having a high resistance to heat.
It is still another object of the invention to provide a magnetoresistance effect element of which the resistance can be greatly changed.
It is a further object of the invention to provide a magnetic head capable of detecting magnetic flux with high sensitivity and of being easy to produce, or having a simple construction.
It is still a further object of the invention to provide a magnetic storage apparatus capable of precisely writing and reading a high-density magnetic recording.
The inventors have studied the shape of the magnetoresistance effect element formed of a multilayered magnetoresistance effect film which has magnetic layers and an intermediate layer of an insulating material such as Al2O3, SiO2, NiO or BN, a semiconductor such as Si, Ge or GaAs, or an antiferromagnetic material such as Cr, inserted between the magnetic layers, and have found that when the element is so constructed and shaped that all the current flowing in the magnetoresistance effect film is sure to be passed through the intermediate layers and that electrodes of nonmagnetic metal (conductor) are connected at least to part of the magnetoresistance effect film, the magnetoresistance effect element can detect the magnetic field from a narrow region with high sensitivity.
The first feature of this invention is that, since at least part of the multilayered magnetoresistance effect film is formed on a conductor of nonmagnetic metal and the film surfaces of all the magnetic layers of the magnetoresistance effect film are disposed substantially at right angles to the surface of a magnetic recording medium or the end surface of the multilayered magnetoresistance effect film is opposed to the magnetic recording medium surface, the area of the magnetic layers of the end surface portion of the magnetoresistance effect film can be extremely reduced, and thus a very small change of the magnetic flux leaking from a high-density recorded magnetic recording medium on which narrow tracks are formed can be detected with high sensitivity and with high resolution.
The magnetoresistance effect element structure according to this invention can be suitably formed of either one of the following magnetoresistance effect films (1) and (2):
(1) A multilayered film having magnetic layers and an intermediate layer of an insulating material such as Al2O3, SiO2, NiO or BN, a semiconductor such as Si, Ge or GaAs, or other materials, inserted between the magnetic layers; for example, a ferromagnetic thin film, using a ferromagnetic spin-dependent tunneling effect, such as Ni/NiO/Co, Fe/Ge/Co, Al/Al2O3/Ni, Coxe2x80x94Al/Al2O3/Ni, Fexe2x80x94C/SiO2/Fexe2x80x94Ru, Fexe2x80x94C/Al2O3/Coxe2x80x94Ni, Fexe2x80x94C/Al2O3/Fexe2x80x94Ru and so on.
(2) A multilayered film having magnetic layers and an intermediate layer of an anti-ferromagnetic material such as Cr inserted between the magnetic layers; for example, a magnetic thin film using antiferromagnetic intermediate layers such as Fe/Cr.
Moreover, in the magnetoresistance effect element of this invention, in order for a very small change of magnetic flux to be detected with high sensitivity and with high resolution to produce a stable reproduced output, the following specific technical means can be employed:
(1) The coercive force of one of a pair of magnetic layers constituting a multilayered magnetoresistance effect film is reduced, so that the difference between the coercive force and that of the other magnetic layer can be increased.
(2) The easy axis directions of a pair of magnetic layers constituting a multilayered magnetoresistance effect film are made perpendicular to each other.
(3) Of a pair of magnetic layers constituting a multilayered magnetoresistance effect film, the angular magnetic anisotropy dispersion xcex190 of at least one magnetic layer is selected to be 10xc2x0 or below.
(4) Of a pair of magnetic layers constituting a multilayered magnetoresistance effect film, at least one magnetic layer is made to be a single magnetic domain.
(5) A lamination comprised of a pair of magnetic layers and an insulating layer constituting a multilayered magnetoresistance effect film is held between layers of high-permeability magnetic materials.
As described above, since the element is so constructed and shaped that the current flowing in the multilayered magnetoresistance effect film is sure to be passed through the intermediate layer constituting the magnetoresistance effect film, and since for example at least a part of the magnetoresistance effect film is formed on a conductor of nonmagnetic metal, the magnetic field from a narrow region can be detected. In other words, when at least a part of the magnetoresistance effect film is formed on an electrode conductor of nonmagnetic metal, the film surfaces of all the magnetic layers constituting the magnetoresistance effect film can be opposed substantially at right angles to the magnetic recording medium surface. Thus, since the area of the magnetic layers of the end surface portion of the magnetoresistance effect film facing the magnetic recording medium can be extremely reduced, the magnetic field from a narrow region can be detected with a high sensitivity. In addition, either one of the multilayered magnetoresistance effect films, or (1) the magnetic thin film using the ferromagnetic spin-dependent tunneling effect and (2) the magnetic thin film using the antiferromagnetic intermediate layers, can be applied to the element structure of this invention.
Moreover, in order for, for example, one of a pair of magnetic layers constituting the multilayered magnetoresistance effect film to be changed in its magnetization direction by the magnetic field leaking from the medium, the coercive force is set to about the leaked magnetic field strength. Also, in order for the other magnetic layer not to be changed in its magnetization direction even if the leaked magnetic field from the medium is applied thereto, the coercive force is set to a sufficiently high value.
If the coercive forces of the pair of magnetic layers are set as above, it is possible to obtain an output that is higher than in the conventional inductive-type thin-film head or magnetoresistance effect head.
Moreover, the magnetic layer which is changed in its magnetization direction by the magnetic field leaking from the medium is required to have a small angular magnetic anisotropy dispersion and a single magnetic domain in order that the magnetization rotation is caused at a time. If this condition is satisfied, the reading sensitivity and stability can be improved.
Moreover, the total film thickness of the multilayered magnetoresistance effect film comprised of a pair of magnetic layers and an insulating layer is reduced to be smaller than the shortest recorded bit length written on the medium, and the multilayered magnetoresistance effect film is held between a pair of high-permeability films, thereby further improving the reading resolution.
In addition, since the junction area between a pair of magnetic layers constituting the multilayered magnetoresistance effect film is reduced, the probability of the occurrence of defects (pinholes) in the insulating layer can be reduced, so that the reproduction sensitivity can be further improved.
The second feature of the invention is that even if the coercive forces of the two magnetic layers of the ferromagnetic spin-dependent tunneling effect film constituting the magnetoresistance effect element are not greatly different (e.g. if the materials of the two layers are the same), application of a bias magnetic field from an antiferromagnetic material to one magnetic layer will enable the magnetic field for changing the magnetization direction of the layer to change, so that the magnetization directions of both layers are antiparallel in a certain range of magnetic field, but are parallel in another range of magnetic field, thus the element exhibiting the magnetoresistance effect.
Moreover, since at least a part of the ferromagnetic spin-dependent tunneling effect film is formed on nonmagnetic metal, the area of the magnetic layers facing the magnetic recording medium can be decreased, so that the magnetic field from a narrow region can be detected.
As described above, even if the coercive forces of the two magnetic layers of the ferromagnetic tunneling effect film are not greatly different (e.g. if the materials of the two layers are the same), application of a bias magnetic field from the antiferromagnetic material to one magnetic layer will enable the magnetic field for changing the magnetization directions of both layers to change. Thus, the magnetization directions of both layers are antiparallel in a certain range of magnetic field, but are parallel in another range of magnetic field, thus the element exhibiting the magnetoresistance effect.
Moreover, since at least a part of the ferromagnetic tunneling effect film is formed on nonmagnetic metal, the area of the magnetic layers facing the magnetic recording medium can be decreased, so that the magnetic field from a narrow region can be detected.
The third feature of the invention is that, since after the study on the multilayered film exhibiting the ferromagnetic spin-dependent tunneling effect, one or more materials for an intermediate layer are selected from a carbide, a boride, a nitride, a phosphide and a compound of group IIIb to Vb elements, the soft magnetic characteristics of the magnetic layers are not deteriorated and the characteristics of the ferromagnetic spin-dependent tunneling element are not changed even when the element is passed through the heating process for magnetic head production.
In other words, when an oxide intermediate layer of NiO or Al2O3 is used, the interface energy is increased in the interface between the magnetic layers and intermediate layer. When the interface energy is high, the number of atoms in the interface tends to decrease, and defects may occur, such as vacancies from which atoms are ejected, so that the soft magnetic characteristics may be deteriorated as described by Nakatani, et al. in J. Appl. Phys., Vol. 66, pp. 4338, 1989, xe2x80x9cChanges in Soft Magnetic Properties of Fe Multilayered Films due to Lattice Mismatches between Fe and Intermediate Layersxe2x80x9d. On the other hand, the intermediate layer of a carbide, a boride, a nitride, a phosphide or a compound of group IIIb to Vb elements has a low interface energy between the magnetic layers. Therefore, the number of atoms in the interface may be large, and thus no defect occurs in the magnetic layers. Moreover, the compound intermediate layer has a high melting point and thus if the element is passed through the heating process for magnetic head production, the elements of the intermediate layer are not diffused into the magnetic layers, so that the ferromagnetic tunneling effect element is not deteriorated. Also, since the intermediate layer is used to form the tunneling junction, it is necessary for it to be made of an insulating material or to have an electrical resistance higher than that of the semiconductor.
In summary, as described above, the intermediate layer of carbide, a boride, a nitride, a phosphide or a compound of group IIIb to Vb elements has a low interface energy between the magnetic layers. Therefore, no defect occurs in the magnetic layers. Moreover, the compound intermediate layer has a high melting point and thus if the element is passed through the heating process for the magnetic head production, the elements of the intermediate layer are not diffused into the magnetic layers, so that the ferromagnetic tunneling effect element is not deteriorated.
The fourth feature of the invention is that, since after the study on the element using the Fe/Cr multilayered film and the element having the magnetoresistance effect due to the multilayered structure such as the ferromagnetic tunneling element, it has been found that the resistances of these elements are low so that a large amount of resistance change cannot be obtained even when the relative resistivity change is high, or that in the element having the Fe/Cr multilayered films and the element having the magnetoresistance effect due to the multilayered structure such as the ferromagnetic tunneling element, the electrical resistance of the whole element can be increased by series connection of a plurality of magnetoresistance effect elements, and that the element is so constructed that electrons are passed a plurality of times through the nonmagnetic layer located at the same distance from the base.
As described above, in the element having the Fe/Cr multilayered films and the element having the magnetoresistance effect due to the multilayered structure such as the ferromagnetic tunneling element, the electrical resistance of the whole element can be increased and a large amount of resistance change can be obtained by series connection of a plurality of magnetoresistance effect elements. Also, since the element is so constructed that electrons are passed a plurality of times through the nonmagnetic layer located at the same distance from the substrate, the electrical resistance of the whole element can be increased and a large amount of resistance change can be obtained without increasing the film thickness of the whole element. Moreover, according to this invention, since the film thickness of the whole element is not changed, the resolution relative to the magnetic field distribution in the wavelength direction is not reduced when the element is used in a magnetic head.
The fifth feature of the invention is that, as an element for detecting the magnetic flux leaking from the magnetic domain recorded on a magnetic recording medium, a plurality of ferromagnetic laminated elements connected in series through a very thin electrically insulating film, semiconductor film or semimetal film can be used in a magnetic head to detect the phenomenon that the tunneling current flowing through the element upon supplying current thereto is changed in accordance with the change of the magnetic field.